1. Field of the Invention
The field of the invention is that of measurement of vibrations. In particular, the field is that of speckle analysis of biological and microscopic systems.
2. Description of the Related Art
The phenomenon of dynamic speckle is observed when an object under investigation is illuminated with coherent laser radiation. Laser-induced speckle patterns have found applications in studying bio-specimens non-invasively. Living cells or tissues of bio-specimens create complex and randomly varying ‘bio-speckles’ that are characteristic signatures of the specimen.
Lasers have found their way in biomedical applications because of the properties of power, high coherence and low beam divergence. When a low power laser illuminates a surface, light is scattered in all directions. These scattered light rays in turn interfere with each other causing a localized microscopic interference pattern called speckle. The term bio-speckle refers to speckle pattern detected on a biological specimen. The speckle pattern has both temporal and spatial characteristics. In the time domain the speckle pattern is directly related to changes taking place that effect the scattering of light. An inanimate object is time-invariant and thus has no temporal component. An animate object, however, will yield a time-varying speckle pattern as the geometry and surface alter. The change may come from the object moving as a whole, or as the compositional elements within move. Regardless of where the dynamic behavior occurs, there is an observed phase shift. In the case of compositional elements moving within a living structure or tissue, a continuously changing pattern will be observed. This ‘boiling’ speckle is referred to as the biospeckle and has been observable in objects such as fruit, vegetables, blood flow, and egg embryos.
This speckle pattern is directly related to the rate at which the compositional elements within the structure move i.e., the bioactivity. Most macroscopic living organisms are composed of a thin semi-permanent membrane (skin) and compositional elements moving within, whether these be blood cells, plasma, chromoplasts in plants, or other smaller parts of the cell. The laser light penetrates past the surface (dermal) layers and into the tissue beneath. Cells are composed of hundreds of smaller components moving within the cytoplasm. It should be a reasonable conjecture that all moving elements do not have the same speed. If the elements are large enough to backwards scatter the light, then each part of the cell that moves should have an observable velocity relationship.
Laser-induced speckle patterns have found applications in studying microscopic vibrations of inanimate systems non-invasively. Several such systems vibrate with one or more frequency of oscillations. These vibrations have very small positional displacements on the order of a few to several nanometers. These systems create temporal varying speckles that are characteristic signatures of their particular systems. In the case of compositional elements moving within a vibrating structure, a continuously changing pattern will be observed. This temporally varying speckle is characteristic to vibrations which have been observable in inanimate objects such as a vibrating surface on a micro-switch, micro-actuator, or micro-motor used in nanotechnology type devices.
However, previous attempts at analyzing speckle patterns have been unsuccessful in providing predictable results. What is needed is a more accurate analysis of vibrations to provide more meaningful evaluations of living structures, tissues, or nanotechnology.